Light emitting device that emits secondary light with a fast response

ABSTRACT

A light emitting device which emits a secondary light with high color purity and has a fast response speed is obtained. A KSF phosphor ( 15 ) which absorbs a part of blue light and emits red light and a CASN phosphor ( 16 ) are distributed in a resin ( 14 ) which seals an LED chip ( 13 ) which emits the blue light. The KSF phosphor ( 15 ) absorbs the blue light and emits the red light by forbidden transition, and the CASN phosphor ( 16 ) absorbs the blue light and emits the red light by allowed transition.

TECHNICAL FIELD

The present invention relates to a light emitting device and anillumination device.

BACKGROUND ART

For a backlight used in a so-called liquid crystal television (TV), anLED chip which emits blue light as primary light, a red phosphor whichis excited by the blue light and emits red light as secondary light, anda green phosphor which emits green light are used. The backlight emitswhite light which is obtained by mixing blue light, green light, and redlight.

PTL 1 discloses a light emitting element which emits white light byexciting, using an LED for emitting blue light, divalent Eu-activatedCaAlSiN₃ (hereinafter, referred to as CASN phosphor) which is anitride-based phosphor for emitting red light, and a green phosphor thatemits green light.

In addition, an Eu-activated β-type SiAlON phosphor disclosed in, forexample, PTL 2 has been appropriately used in the related art as aphosphor which emits green light.

In a case where an illumination device which emits white light bycombining a blue LED, a red phosphor, and a green phosphor is used as alight source of a backlight of a liquid crystal television, there is atendency for color reproducibility of the liquid crystal television tobe improved by using a phosphor having a narrower peak wavelength of alight spectrum.

However, in a case where the CASN phosphor which is a phosphor disclosedin PTL 1 is used, a wavelength width of the light spectrum of the redphosphor is equal to or greater than 80 nm, and thus, the colorreproducibility of red is not sufficient.

Accordingly, in order to realize a display device such as a liquidcrystal television which can display deep red, development of abacklight which uses a Mn⁴⁺-activated K₂SiF₆ phosphor (hereinafter,referred to as KSF phosphor) disclosed in PTL 3 is in progress. A KSFphosphor has a spectrum of peak wavelength narrower than that of a CASNphosphor and can have further improved color reproducibility than therelated art.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2006-16413(published on Jan. 19, 2006)

PTL 2: Japanese Unexamined Patent Application Publication No.2005-255895 (published on Sep. 22, 2005)

PTL 3: Japanese Unexamined Patent Application Publication No. 2010-93132(published on Apr. 22, 2010)

PTL 4: International Publication No. WO2009/110285 (published on Sep.11, 2009)

PTL 5: Japanese Unexamined Patent Application Publication No.2009-528429 (translation of PCT Application published on Aug. 6, 2009)

PTL 6: Japanese Unexamined Patent Application Publication No. 2007-49114(published on Feb. 22, 2007)

SUMMARY OF INVENTION Technical Problem

Here, the majority of liquid crystal televisions display images at 60Hz, 120 Hz, or 240 Hz which is an integer multiple of a frame frequencyof a video signal. It is possible to realize a display in which anunwanted image is not shown to a user by temporarily extinguishing abacklight based on the fact that an LED can be illuminated orextinguished at a high speed.

For example, an afterimage is reduced by temporarily extinguishing abacklight, while an image of the next frame is redisplayed on a liquidcrystal screen. In addition, in a three-dimensional (3D) display of aframe sequential method by which an image for the right eye and an imagefor the left eye are alternately displayed, the backlight is temporarilyextinguished until the images are displayed on the entire screen, andthus, it is possible to perform a function in which video that isobtained by mixing images of the right eye and the left eye is notshown.

In a case where this function is performed, a pulse width modulation(PWM) drive method in which illumination and extinguishing are repeatedis used as an LED drive method used for a backlight, but timing of theillumination and extinguishing is synchronized with a display of aliquid crystal panel, and thus, a PWM period becomes 60 Hz, 120 Hz, or240 Hz which is an integer multiple of the frame frequency of the videosignal.

If the red phosphor (KSF phosphor) described in PTL 3 is used, colorreproducibility by obtaining light having a narrow spectrum can beimproved, but the KSF phosphor has a time (also referred to as afterglowtime) of approximately 10 [ms] which is the time taken for the lightintensity to become 1/e (e is a natural logarithm base) and isapproximately 100 to 1000 times longer than the afterglow time of a CASNphosphor.

Accordingly, in a case where an LED is illuminated or extinguished at adimming frequency (PWM dimming) synchronized with a display of a liquidcrystal panel, even at timing in which blue light having a rectangularwaveform from an LED chip of the LED is extinguished, as illustrated inFIG. 17, there is an afterglow of red light from a KSF phosphor which isexcited by blue light from the LED chip and emits light. Due to theafterglow of red light from the KSF phosphor, an abnormality such as aphenomenon in which a displayed image is shown in color or a phenomenonin which images for the right eye and the left eye are mixed to be shownat the time of a 3D display, that is, a so-called crosstalk phenomenon,occurs. For example, this crosstalk occurs remarkably in an image or thelike in which telop characters flow on the screen, and a part of thetelop is shown in red.

FIG. 17 illustrates a response waveform of the KSF phosphor when abacklight having a PWM drive frequency of 120 Hz and a duty of 20% isdriven.

The present invention is to solve the above problems, and an objectivethereof is to obtain a light emitting device which emits the secondarylight with high color purity and has a fast response speed and to obtainan illumination device.

Solution to Problem

According to an aspect of the present invention, a light emitting deviceincludes a light emitting element which emits primary light; a resinwhich seals the light emitting element; and first and second phosphorswhich are distributed in the resin, absorb a part of the primary light,and emit secondary light having a wavelength longer than that of theprimary light. The first phosphor absorbs the primary light and emitsthe secondary light by forbidden transition, and the second phosphorabsorbs the primary light and emits the secondary light by allowedtransition.

Advantageous Effects of Invention

According to an aspect of the present invention, it is possible toobtain a light emitting device which emits the secondary light with highcolor purity and has a fast response speed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an LED in an illumination device accordingto Embodiment 1.

FIG. 2(a) is an expanded plan view illustrating a part of theillumination device which uses the LED according to Embodiment 1, andFIG. 2(b) is a sectional view of the illumination device illustrated inFIG. 2(a).

FIG. 3 is a block diagram illustrating a configuration of an LED drivecontrol unit which controls driving of the LED.

FIG. 4 is a diagram illustrating a light emission state of blue lightand red light of the LED according to a PWM signal.

FIG. 5 is a diagram illustrating a light spectrum of a KSF phosphor.

FIG. 6 is a diagram illustrating a light spectrum of a CASN phosphor.

FIG. 7 is a diagram illustrating a light spectrum of an LED including agreen phosphor in a case where an intensity ratio of peak wavelengthbetween the KSF phosphor and the CASN phosphor is variously changed.

FIG. 8 is a diagram illustrating a light spectrum of the LED includingthe green phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor and the CASN phosphor is furtherchanged.

FIG. 9 is a diagram illustrating a light spectrum of the LED withoutincluding the green phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor and the CASN phosphor is variouslychanged.

FIG. 10 is a diagram illustrating measurement results of afterglow timeof a red phosphor in a case where the intensity ratio of peak wavelengthbetween the KSF phosphor and the CASN phosphor is KSF:CASN=100:0.

FIG. 11 is a diagram illustrating measurement results of afterglow timeof the red phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor and the CASN phosphor isKSF:CASN=75:25.

FIG. 12 is a diagram illustrating measurement results of afterglow timeof the red phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor and the CASN phosphor isKSF:CASN=50:50.

FIG. 13(a) is an expanded plan view illustrating a part of a lightsource unit in an illumination device according to Embodiment 2, andFIG. 13(b) is a sectional view of the illumination device.

FIG. 14 is a sectional view of an LED in the illumination deviceaccording to Embodiment 2.

FIG. 15 is a block diagram illustrating a configuration of an LED drivecontrol unit which controls driving of a first LED chip and a second LEDchip in the LED according to Embodiment 2.

FIG. 16 is a diagram illustrating a relationship between a PWM signaland drive states of the first LED chip and the second LED chip.

FIG. 17 is a diagram illustrating light emission states of blue lightand red light of an LED according to the PWM signal in the LED of therelated art which uses a KSF phosphor.

FIG. 18 is a diagram obtained by simulating light emission states ofblue light and red light of the LED according to the PWM signal, usingthe KSF phosphor and a phosphor having an afterglow time which isassumed to be 100 μs.

DESCRIPTION OF EMBODIMENTS Embodiment 1

(Configuration of Illumination Device 1)

First, the illumination device 1 which uses an LED (light emittingdevice) 11 according to the present embodiment will be described. FIG.2(a) is an expanded plan view illustrating a part of the illuminationdevice 1 which uses the LED 11 according to Embodiment 1, and FIG. 2(b)is a sectional view of the illumination device 1 illustrated in FIG.2(a).

As illustrated in FIGS. 2(a) and 2(b), the illumination device 1includes a substrate 2, multiple LEDs 11 and a light guiding plate 5.The illumination device 1 also includes an LED drive control unit (referto FIG. 3), which is not illustrated in FIG. 2, for controlling drivingof multiple LEDs 11.

The light guiding plate 5 has a rectangular shape overall and is atransparent member having a predetermined thickness. The light guidingplate 5 has a structure in which light is emitted from each portion of alight emitting surface 5 b such that light which is incident from alight incident portion 5 a is emitted in a planar form, and the lightguiding plate 5 is formed of a transparent material such as acryl. Inaddition, an end surface on a side of the light guiding plate 5functions as the light incident portion 5 a on which light is incident.

The substrate 2 is formed as an elongated rectangle (strip shape). Inthe substrate 2, printed wires (not illustrated) through which power istransferred to the LED 11 are formed on a mounting surface on whichmultiple LEDs 11 are mounted. In addition, a positive terminal (notillustrated) and a negative terminal (not illustrated) which are coupledto the printed wires are provided at both end portions or one endportion of the substrate 2. Wires through which power is supplied fromthe outside are coupled to the positive terminal and the negativeterminal, and thereby the LED 11 receives power.

The multiple LEDs 11 are mounted in a line on the substrate 2 in alongitudinal direction of the substrate 2. The multiple LEDs 11 arecoupled in series in a longitudinal direction of the substrate 2.

A light source unit 7 is formed by the substrate 2 and the LED 11. Inthe light source unit 7, a light emitting surface of each of themultiple LEDs 11 faces the light incident portion 5 a such that lightemitted from an LED chip (light emitting element) 13 of each of themultiple LEDs 11 is incident on the light incident portion 5 a of thelight guiding plate 5, and the light source unit 7 is disposed at alocation close to the light guiding plate 5.

(Configuration of LED 11)

A configuration of the LED 11 will be described in detail with referenceto FIG. 1 and FIG. 2. FIG. 1 is a sectional view of the LED 11 in theillumination device 1.

As illustrated in FIG. 2(a), the LED 11 has a light emitting surfacehaving a rectangular shape as an example, and the LED chip 13 is mountedin the center. In addition, as illustrated in FIG. 1, the LED 11includes a package 12, the LED chip 13, a resin 14, a KSF phosphor(first phosphor) 15, a CASN phosphor (second phosphor) 16, and a greenphosphor 17.

The package 12 has a cavity (concave portion) 12 a which is a concaveportion. The cavity 12 a is a space which is provided in the package 12such that the LED chip 13 is mounted on a bottom surface in the concaveportion and a side surface of the concave portion is used as areflecting surface. The package 12 is formed of a nylon-based materialand is provided by insert molding such that a lead frame, which is notillustrated, is exposed on the bottom surface of the cavity 12 a of thepackage 12. The lead frame is divided into two parts at an exposedportion.

The package 12 includes a reflecting surface which forms an inner sidesurface of the cavity 12 a which is a concave portion. It is preferablethat the reflecting surface is formed of a metal film with highreflectance including Ag or Al, or white silicone, such that light whichis emitted from the LED chip 13 is reflected to the outside of the LED11.

The LED chip 13 is, for example, a gallium nitride (GaN)-basedsemiconductor light emitting element containing a conductive substrate,and while not illustrated, a bottom surface electrode is formed on abottom surface of the conductive substrate and an upper electrode isformed on a reverse surface thereof. The emitted light (primary light)of the LED chip 13 is blue light in a range of 430 nm to 480 nm and hasa peak wavelength in the vicinity of 450 nm.

The LED chip 13 (blue LED chip) is die-bonded to one side of the exposedportion in the lead frame by a material having low conductivity.Furthermore, in the LED chip 13, the upper electrode of the LED chip 13and the other side of the exposed portion in the lead frame aredie-bonded by a wire, which is not illustrated. In this way, the LEDchip 13 is electrically coupled to the lead frame. Here, the LED chiprespectively having electrodes on the upper surface and a lower surfaceis described, but it is also possible to use an LED having twoelectrodes on the upper surface.

The cavity 12 a is filled with the resin 14, and thereby the cavity 12 ain which the LED chip 13 is disposed is sealed. In addition, since theresin 14 needs to have high durability with respect to primary lightwith a long wavelength, a silicone resin is appropriately used. Asurface of the resin 14 forms a light emitting surface from which lightis emitted.

A first phosphor and a second red phosphor which are excited by firstlight emitted from the LED chip 13 are two types of red phosphor andemit red light, and a green phosphor 17 which is excited by the firstlight that is emitted from the LED chip 13, are distributed in the resin14 as secondary light. The first red phosphor is a phosphor(hereinafter, there is a case of being referred to as a phosphor of aforbidden transition type) which emits red light by forbiddentransition, and the second red phosphor is a phosphor (hereinafter,there is a case of being referred to as a phosphor of an allowedtransition type) which emits red light by allowed transition. The redphosphors distributed in the resin 14 may be at least the phosphor of aforbidden transition type and the phosphor of an allowed transition typeof two types and may be red phosphors of three types or more. Inaddition, the green phosphor 17 may or may not be distributed in theresin 14 as necessary.

The KSF phosphor 15 is distributed in the resin 14 and is an example ofthe first red phosphor which emits red light by the forbiddentransition. The KSF phosphor 15 is excited by blue light which is aprimary light and emits red (peak wavelength is equal to or longer than600 nm and is equal to or shorter than 780 nm) secondary light having awavelength longer than that of the primary light. The KSF phosphor 15 isa phosphor having a Mn⁴⁺-activated K₂SiF₆ structure.

The KSF phosphor 15 emits red light which has a wavelength width of peakwavelength that is narrowed to approximately 30 nm or less and has highpurity.

The afterglow time of the KSF phosphor 15 which is the time required forthe light intensity of secondary light from the KSF phosphor 15 tobecome 1/e (e is a natural logarithm base) when primary light from theLED chip 13 is extinguished, is approximately 7 ms to 8 ms. In addition,in order for the secondary light from the KSF phosphor 15 to be almostcompletely on or extinguished, approximately 10 ms is needed.

The first red phosphor (first phosphor) which is distributed in theresin 14 may be a phosphor which emits red light by forbiddentransition. Particularly, it is preferable that the first red phosphoris formed of a phosphor material having a narrow spectrum of wavelengthwidth of peak wavelength equal to or narrower than 30 nm.

In addition to the phosphor having the Mn⁴⁺-activated K₂SiF₆ structure,a Mn⁴⁺-activated Mg fluorogermanate phosphor or the like can be used asa material which can be used as the first red phosphor having a narrowwavelength width of peak wavelength. Furthermore, the first red phosphorwhich emits red light by forbidden transition may be one of theMn⁴⁺-activated complex fluoride phosphors represented by followinggeneral formulas (A1) to (A8)

A₂[MF₅]:Mn⁴⁺  general formula (A1)

(in the above general formula (A1), A is selected from any one of Li,Na, K, Rb, Cs, and NH₄ or from a combination of these, and M is selectedfrom any one of Al, Ga, and In or from a combination of these)

A₃[MF₆]:Mn⁴⁺  general formula (A2)

(in the above general formula (A2), A is selected from any one of Li,Na, K, Rb, Cs, and NH₄ or from a combination of these, and M is selectedfrom any one of Al, Ga, and In or from a combination of these)

Zn₂[MF₇]:Mn⁴⁺  general formula (A3)

(in the above general formula (A3), M in [ ] is selected from any one ofAl, Ga, and In or from a combination of these)

A[In₂F₇]:Mn⁴⁺  general formula (A4)

(in the above general formula (A4), A is selected from any one of Li,Na, K, Rb, Cs, and NH₄ or from a combination of these)

A₂[MF₆]:Mn⁴⁺  general formula (A5)

(in the above general formula (A5), A is selected from any one of Li,Na, K, Rb, Cs, and NH₄, or from a combination of these, and M isselected from any one of Ge, Si, Sn, Ti, and Zr or from a combination ofthese)

E[MF₆]:Mn⁴⁺  general formula (A6)

(in the above general formula (A6), E is selected from any one of Mg,Ca, Sr, Ba, and Zn or from a combination of these, and M is selectedfrom any one of Ge, Si, Sn, Ti, and Zr or from a combination of these)

Ba_(0.65)Zr_(0.35)F_(2.70):Mn⁴⁺  general formula (A7)

A₃[ZrF₇]:Mn⁴⁺  general formula (A8)

(in the above general formula (A8), A is selected from any one of Li,Na, K, Rb, Cs, and NH₄ or from a combination of these)

Furthermore, the first red phosphor which is distributed in the resin 14may be a tetravalent manganese-activated fluoride tetravalent metal saltphosphor in actuality represented by, for example, the following generalformula (A9) or the general formula (A10), in addition to being thephosphor having the Mn⁴⁺-activated K₂SiF₆ structure.

MII₂(MIII_(1-h)Mn_(h))F₆   general formula (A9)

In the general formula (A9), MII indicates at least one type of Alkalimetal element which is selected from Li, Na, K, Rb, and Cs, and it ispreferable that MII is K with regard to brightness and stability ofpowder characteristics. In addition, in the general formula (A9), MIIIindicates at least one type of tetravalent metal element which isselected from Ge, Si, Sn, Ti, and Zr, and it is preferable that MIII isTi with regard to brightness and stability of powder characteristics.

In the general formula (A9), a value of h which indicates a compositionratio (concentration) of Mn is 0.001≤h≤0.1. In a case where the value ofh is less than 0.001, there is an abnormality of sufficient brightnessbeing not obtained. In addition, in a case where the value of h exceeds0.1, there is an abnormality of brightness being significantly reduceddue to concentration quenching or the like. It is preferable that thevalue of h is 0.005≤h≤0.5 with regard to brightness and stability ofpowder characteristics.

Specifically, K₂(Ti_(0.99)Mn_(0.01))F₆, K₂(Ti_(0.9)Mn_(0.1))F₆,K₂(Ti_(0.999)Mn_(0.001))F₆, Na₂(Zr_(0.98)Mn_(0.02))F₆,Cs₂(Si_(0.95)Mn_(0.05))F₆, Cs₂(Sn_(0.98)Mn_(0.02))F₆,K₂(Ti_(0.88)Zr_(0.10)Mn_(0.02))F₆, Na₂(Ti_(0.25)Sn_(0.20)Mn_(0.05))F₆,Cs₂(Ge_(0.999)Mn_(0.001))F₆,(K_(0.80)Na_(0.20))₂(Ti_(0.69)Ge_(0.30)Mn_(0.01))F₆, or the like can beused as the first red phosphor which is represented by the generalformula (A9), but the first red phosphor is not limited to this.

MIV(MIII_(1-h)Mn_(h))F₆   general formula (A10)

In the general formula (A10), MIII indicates at least one type oftetravalent metal element which is selected from Ge, Si, Sn, Ti, and Zr,as well as MIII in the aforementioned general formula (A9), and it ispreferable that MIII is Ti for the same reason. In addition, in thegeneral formula (A10), MIV indicates at least one type of alkali earthmetal element which is selected from Mg, Ca, Sr, Ba, and Zn, and it ispreferable that MIV is Ca with regard to brightness and stability ofpowder characteristics. In addition, in the general formula (A10), avalue of h which indicates a composition ratio (concentration) of Mn is0.001≤h≤0.1 in the same manner as in the aforementioned general formula(A9), and for the same reason, it is preferable that the value of h is0.005≤h≤0.5.

Specifically, Zn(Ti_(0.98)Mn_(0.02))F₆, Ba(Zr_(0.995)Mn_(0.005))F₆,Ca(Ti_(0.995)Mn_(0.005))F₆, Sr(Zr_(0.98)Mn_(0.02))F₆, or the like can beused as the first red phosphor which is represented by the generalformula (A10), but the first red phosphor is not limited to this.

The CASN phosphor 16 is distributed in the resin 14 and is an example ofthe second red phosphor which emits red light by allowed transition. TheCASN phosphor 16 is excited by blue light which is a primary light andemits red (peak wavelength is equal to or longer than 600 nm and isequal to or shorter than 780 nm) secondary light having a wavelengthlonger than that of the primary light. The CASN phosphor 16 is aphosphor having a divalent Eu-activated CaAlSiN₃ structure.

The CASN phosphor 16 has a wavelength width of peak wavelength greaterthan that of the KSF phosphor 15. However, the afterglow time of theCASN phosphor 16 which is the time required for the light intensity ofsecondary light from the CASN phosphor 16 to become 1/e (e is a naturallogarithm base) when primary light from the LED chip 13 is extinguishedis approximately 1 μs to 10 μs. The CASN phosphor 16 has a responsespeed faster than that of the KSF phosphor 15.

Since the afterglow time of the KSF phosphor 15 (first phosphor) isapproximately 10 ms, the afterglow of the CASN phosphor 16 (secondphosphor) is 1/10000 to 1/1000 of the afterglow time of the KSFphosphor. That is, the response speed of the second phosphor is equal toor faster than 1000 times the response speed of the first phosphor, andit is preferable that the response speed of the second phosphor is equalto or faster than 10000 times the response speed of the first phosphor.

A material which can be used for the second red phosphor may be adivalent Eu-activated nitride phosphor in actuality represented by thefollowing general formula (B1), in addition to the phosphor having thedivalent Eu-activated CaAlSiN₃ structure.

(XIII_(1-j)Eu_(j))XIVSiN₃   general formula (B1)

In the general formula (B1), XIII indicates at least one type of elementwhich is selected from Mg, Ca, Sr, and Ba, XIV indicates at least onetype of element which is selected from Al, Ga, In, Sc, Y, La, Gd, andLu, and j indicates a number which satisfies 0.001≤j≤0.05.

Specifically, (Ca_(0.98)Eu_(0.02))AlSiN₃, (Ca_(0.985)Eu_(0.015))AlSiN₃,(Ca_(0.94)Sr_(0.05)Eu_(0.01))AlSiN₃,(Ca_(0.99)Eu_(0.01))Al_(0.90)Ga_(0.10)SiN₃, (Ca_(0.98)Eu_(0.02))AlSiN₃,(Ca_(0.97)Ba_(0.01)Eu_(0.02))Al_(0.99)In_(0.01)SiN₃,(Ca_(0.98)Eu_(0.02))AlSiN₃, (Ca_(0.99)Eu_(0.01))AlSiN₃, or the like canbe used as the second red phosphor which is represented by the generalformula (B1), but the second red phosphor is not limited to this.

The green phosphor 17 (green phosphor) is distributed in the resin 14.The green phosphor 17 is a phosphor which is excited by blue light whichis a primary light, and the green phosphor 17 emits green (peakwavelength is equal to or longer than 500 nm and is equal to or shorterthan 550 nm) secondary light having a wavelength longer than that of theprimary light.

The green phosphor 17 may be β-type SiAlON which is a divalentEu-activated oxynitride phosphor represented by the following generalformula (C1) or a divalent Eu-activated silicate phosphor represented bythe following general formula (C2).

EuaSibAlcOdNe   general formula (C1)

In the general formula (C1), a value of a which indicates a compositionratio (concentration) of Eu is 0.005≤a≤0.4. In a case where the value ofa is less than 0.005, sufficient brightness is not obtained. Inaddition, in a case where the value of a exceeds 0.4, brightness issignificantly reduced due to concentration quenching or the like. Inaddition, it is preferable that the value of a in the aforementionedgeneral formula (C1) is 0.01≤a≤0.2 with regard to stability of powdercharacteristics, and homogeneity of the basic material. In addition, inthe general formula (C1), b indicating a composition ratio(concentration) of Si and c indicating a composition ratio(concentration) of Al are numbers which satisfy b+c=12, and d indicatinga composition ratio (concentration) of O and e indicating a compositionratio (concentration) of N are numbers which satisfy d+e=16.

Specifically, Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95),Eu_(0.10)Si_(11.00)Al_(1.00)O_(0.10)N_(15.90),Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70),Eu_(0.15)Si_(10.00)Al_(2.00)O_(0.20)N_(15.80),Eu_(0.01)Si_(11.60)Al_(0.40)O_(0.01)N_(15.99),Eu_(0.005)Si_(11.70)Al_(0.30)O_(0.03)N_(15.97) or the like can be usedas the green phosphor 17 which is represented by the general formula(C1), but the green phosphor 17 is not limited to this.

2(Ba_(1-f-g)YI_(f)Eu_(g))O.SiO₂   general formula (C2)

In the general formula (C2), YI indicates at least one type of Alkaliearth metal element which is selected from Mg, Ca, and Sr, and it ispreferable that YI is Sr in order to obtain highly efficient mother. Inthe general formula (C2), a value of f which indicates a compositionratio (concentration) of YI is 0<f≤0.55, and since the value of f iswithin a range thereof, it is possible to obtain green light in a rangeof 510 nm to 540 nm. In a case where the value of f exceeds 0.55,yellowish green light is emitted, and color purity is degraded.Furthermore, it is preferable that the value of f is within a range of0.15≤f≤0.45 from a viewpoint of efficiency and color purity. Inaddition, in the general formula (C2), a value of g which indicates acomposition ratio (concentration) of Eu is 0.03≤g≤0.10. In a case wherea value of g is less than 0.03, sufficient brightness is not obtained.In a case where the value of g exceeds 0.10, brightness is significantlyreduced due to concentration quenching or the like. In addition, it ispreferable that the value of g is within a range of 0.04≤g≤0.08 withregard to brightness and stability of powder characteristics.

Specifically, 2(Ba_(0.70)Sr_(0.26)Eu_(0.04)).SiO₂,2(Ba_(0.57)Sr_(0.38)Eu_(0.05))O.SiO₂,2(Ba_(0.53)Sr_(0.43)Eu_(0.04))O.SiO₂,2(Ba_(0.82)Sr_(0.15)Eu_(0.03))O.SiO₂,2(Ba_(0.46)Sr_(0.49)Eu_(0.05))O.SiO₂,2(Ba_(0.59)Sr_(0.35)Eu_(0.06))O.SiO₂,2(Ba_(0.52)Sr_(0.40)Eu_(0.08))O.SiO₂,2(Ba_(0.85)Sr_(0.10)Eu_(0.05))O.SiO₂,2(Ba_(0.47)Sr_(0.50)Eu_(0.03))O.SiO₂,2(Ba_(0.54)Sr_(0.36)Eu_(0.10))O.SiO₂,2(Ba_(0.69)Sr_(0.25)Ca_(0.02)Eu_(0.04))O.SiO₂,2(Ba_(0.56)Sr_(0.38)Mg_(0.01)Eu_(0.05))O.SiO₂,2(Ba_(0.81)Sr_(0.13)Mg_(0.01)Ca_(0.01)Eu_(0.04))O.SiO₂ or the like canbe used as the green phosphor 17 which is represented by the generalformula (C2), but the green phosphor 17 is not limited to this.

In addition, the green phosphor 17 may be a divalent Eu-activatedsilicate phosphor which is represented by the following general formula(C3).

2(M1_(1-g),Eu_(g))O.SiO₂   general formula (C3)

In the general formula (C3), M1 indicates at least one type of elementwhich is selected from Mg, Ca, Sr, and Ba, and g indicates a numberwhich satisfies 0.005≤g≤0.10.

A so-called BOSE Alkali earth metal silicate phosphor which isrepresented by the general formula (C3) is a phosphor of an allowedtransition type in which the afterglow time which is the time requiredfor the light intensity to become 1/e is equal to or less than 10 μs, aswell as the CASN phosphor.

In the LED 11 having the aforementioned configuration, the primary light(blue light) which is emitted from the LED chip 13 passes through theresin 14. A part thereof excites the KSF phosphor 15 thereby beingconverted into secondary light (red light), excites the CASN phosphor 16thereby being converted into secondary light (red light), and excitesthe green phosphor 17 thereby being converted into secondary light(green light). In this way, white light W0, which is obtained by mixingthe primary blue light and the secondary red and green light, is emittedfrom the LED 11 to the outside of the LED 11.

In the LED 11, a mixture ratio of the green phosphor 17 and the redphosphor (first red phosphor and second red phosphor) is notparticularly limited, but it is preferable that the mixture ratio of thegreen phosphor 17 to the red phosphor is set to a range of 5% to 70% byweight ratio, and it is more preferable that the mixture is set to arange of 15% to 45%. In addition, the mixture ratio of the first redphosphor and the second red phosphor will be described below.

(Configuration of LED Drive Control Unit 1)

FIG. 3 is a block diagram illustrating a configuration of an LED drivecontrol unit 21 which controls driving of the LED 11. The illuminationdevice 1 includes the LED drive control unit 21 illustrated in FIG. 3.

As illustrated in FIG. 3, the LED drive control unit 21 includes adimming control unit (pulse width modulation signal generation means)22, a constant current circuit 23, and an LED circuit 25. The LEDcircuit 25 is a series circuit of the LED chip 13 mounted on thesubstrate 2.

The dimming control unit 22 controls illumination time of the LED chip13 of the LED circuit 25 according to PWM control. For this reason, thedimming control unit 22 includes a PWM circuit (not illustrated) whichgenerates a PWM signal that is provided to the LED circuit 25. The PWMcircuit changes a duty ratio of the PWM signal according to instructionfrom the outside.

The constant current circuit 23 generates a constant current which flowsthrough the LED circuit 25, based on the PWM signal which is suppliedfrom the dimming control unit 22. While the constant current circuit 23is on during a period in which the PWM signal has an H level therebysupplying a constant current to the LED circuit 25, the constant currentcircuit 23 is off during a period in which the PWM signal has an L levelthereby stopping supply of a constant current to the LED circuit 25.

In the LED drive control unit 21 having the aforementionedconfiguration, the constant current which is supplied from the constantcurrent circuit 23 to the LED circuit 25 is controlled by the PWM signalwhich is controlled by the dimming control unit 22. By doing so, lightintensity of the LED chip 13 is controlled.

(With Respect to Light Emission State and Mixture of Red Phosphor)

FIG. 4 is a diagram illustrating a light emission state of the bluelight and the red light of the LED 11 according to the PWM signal. InFIG. 4, light emission of the LED chip represents a light emission stateof the blue light which is emitted from the LED chip 13, and lightemission of the red phosphor represents a light emission state of thered light that is emitted from the KSF phosphor 15 and the CASN phosphor16 in which excitation emission is performed by the blue light emittedfrom the LED chip 13. In addition, a frequency and duty of the PWMsignal which is supplied from the constant current circuit 23 to the LEDcircuit 25 are respectively 120 Hz and 20%, and a light intensity ratiobetween the KSF phosphor 15 and the CASN phosphor 16 is 50:50.

FIG. 5 is a diagram illustrating a light spectrum of the KSF phosphor15. FIG. 6 is a diagram illustrating a light spectrum of the CASNphosphor 16.

As illustrated in FIG. 4, the LED chip 13 emits light such that a squarewave corresponding to on and off of the PWM signal is generated. Inaddition, it can be seen that a rising edge and a falling edge of thelight emitted from the phosphor containing two types of phosphors whichare the KSF phosphor 15 and the CASN phosphor 16 are steeper than arising edge and a falling edge of the light emitted from the redphosphor composed of only the KSF phosphor illustrated in FIG. 17.

That is, it can be seen that after the light emission of the LED chip isoff, the afterglow of the red phosphor containing two types of phosphorswhich are the KSF phosphor 15 and the CASN phosphor 16 illustrated inFIG. 4 is reduced more than that of the red phosphor composed of onlythe KSF phosphor illustrated in FIG. 17.

In a case where a light intensity ratio between the KSF phosphor 15 andthe CASN phosphor 16 is KSF:CASN=50:50, a mixture ratio (weight %) ofthe respective phosphors distributed in the LED 11 is as follows.

KSF phosphor:100

CASN phosphor:13.7

Green phosphor:75.7

In addition, the mixture ratio of the green phosphors needs to beappropriately changed by chromaticity of the LED chip 13.

As illustrated in FIG. 5 and FIG. 6, it can be seen that the KSFphosphor 15 which is a phosphor of a forbidden transition type has anarrow spectrum whose peak wavelength width near 630 nm is narrower thanthat of the CASN phosphor 16 which is a phosphor of an allowedtransition type. It is preferable that a wavelength width of peakwavelength of the light spectrum is approximately equal to or less than30 nm, like in the KSF phosphor 15. In this way, proportion including awavelength band of color other than a wavelength band of red aiming toemit light is low in a light spectrum which is a spectrum having anarrow wavelength width of peak wavelength of a light spectrum. Inaddition, a wavelength band of red to be a target is more clearlyseparated from a wavelength band of color other than that. For thisreason, it is possible to obtain the LED 11 with wide colorreproducibility.

FIG. 7 to FIG. 9 illustrate light spectrums in a case where an intensityratio of peak wavelength between the KSF phosphor 15 and the CASNphosphor 16 is variously changed.

FIG. 7 is a diagram illustrating a light spectrum of the LED 11including the green phosphor 17 in a case where an intensity ratio ofpeak wavelength between the KSF phosphor 15 and the CASN phosphor 16 isvariously changed.

FIG. 8 is a diagram illustrating a light spectrum of the LED 11including the green phosphor 17 in a case where the intensity ratio ofpeak wavelength between the KSF phosphor 15 and the CASN phosphor 16 isfurther changed.

FIG. 9 is a diagram illustrating a light spectrum of the LED 11 withoutincluding the green phosphor 17 in a case where the intensity ratio ofpeak wavelength between the KSF phosphor 15 and the CASN phosphor 16 isvariously changed.

Since a light spectrum is changed depending on target chromaticity, thelight spectrums illustrated in FIG. 7 and FIG. 9 are just examples.

In FIG. 7, the intensity ratio of peak wavelength between the KSFphosphor 15 and the CASN phosphor 16, which is denoted by respectivespectrums SA1 to SA3, is as follows. In addition, in FIG. 7, blue lightemitted from the LED chip 13 and green light emitted from the greenphosphor 17 are also included.

Spectrum SA1 . . . KSF:CASN=100:0

Spectrum SA2 . . . KSF:CASN=60:40

Spectrum SA3 . . . KSF:CASN=50:50

In FIG. 8, the intensity ratio of peak wavelength between the KSFphosphor 15 and the CASN phosphor 16, which is denoted by respectivespectrums SB1 to SB5, is as follows. In addition, in FIG. 8 the bluelight emitted from the LED chip 13 and the green light emitted from thegreen phosphor 17 are also included.

Spectrum SB1 . . . KSF:CASN=0:100

Spectrum SB2 . . . KSF:CASN=100:0

Spectrum SB3 . . . KSF:CASN=25:75

Spectrum SB4 . . . KSF:CASN=50:50

Spectrum SB5 . . . KSF:CASN=75:25

In FIG. 9, the intensity ratio of peak wavelength between the KSFphosphor 15 and the CASN phosphor 16, which is denoted by respectivespectrums SB6 to SB10, is as follows. In addition, in FIG. 9 the bluelight emitted from the LED chip 13 is included, but the green lightemitted from the green phosphor 17 is not included.

Spectrum SB6 . . . KSF:CASN=0:100

Spectrum SB7 . . . KSF:CASN=100:0

Spectrum SB8 . . . KSF:CASN=25:75

Spectrum SB9 . . . KSF:CASN=50:50

Spectrum SB10 . . . KSF:CASN=75:25

As illustrated in FIG. 7 to FIG. 9, it can be seen that, in the redlight in which lights emitted from each of the KSF phosphor 15 and theCASN phosphor 16 are mixed, as components of the light emitted from theKSF phosphor 15 increase, a light spectrum is obtained which has anarrow width of light spectrum that peaks near 630 nm and also has highintensity of the peak.

FIG. 10 to FIG. 12 illustrate measurement results of the afterglow timeof the red phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor 15 and the CASN phosphor 16 ischanged.

FIG. 10 is a diagram illustrating measurement results of the afterglowtime of the red phosphor in a case where the intensity ratio of peakwavelength between the KSF phosphor 15 and the CASN phosphor 16 isKSF:CASN=100:0. FIG. 11 is a diagram illustrating measurement results ofthe afterglow time of the red phosphor in a case where the intensityratio of peak wavelength between the KSF phosphor 15 and the CASNphosphor 16 is KSF:CASN=75:25. FIG. 12 is a diagram illustratingmeasurement results of the afterglow time of the red phosphor in a casewhere the intensity ratio of peak wavelength between the KSF phosphor 15and the CASN phosphor 16 is KSF:CASN=50:50.

In FIG. 10 to FIG. 12, time is denoted by the horizontal axis, and lightintensity is denoted by the vertical axis. XA denotes start time of afalling edge of a red light emitted from a red phosphor, and YA denoteslight intensity in the time XA. YA is light intensity of peak of the redphosphor. YB denotes light intensity when the light intensity from YA is1/e, and XB denotes time of the intensity YB.

In FIG. 10, elapse time (elapse time from time XA to time XB) that istaken from light intensity YA which is the peak intensity of the redphosphor to intensity YB which is 1/e of the intensity is 7.61 ms.

In FIG. 11, the elapse time (elapse time from time XA to time XB) thatis taken from the light intensity YA which is the peak intensity of thered phosphor to the intensity YB which is 1/e of the intensity is 4.22ms.

In FIG. 12, the elapse time (elapse time from time XA to time XB) thatis taken from the light intensity YA which is the peak intensity of thered phosphor to the intensity YB which is 1/e of the intensity is 0.0155ms.

As illustrated in FIG. 10 to FIG. 12, it can be seen that, in the redlight in which lights emitted from each of the KSF phosphor 15 and theCASN phosphor 16 are mixed, as components of the light emitted from theCASN phosphor 16 increase, the elapse time is shortened.

In the above description, the combination of the KSF phosphor 15 and theCASN phosphor 16 is mainly described as the combination of the first redphosphor and the second red phosphor. However, the combination of thefirst red phosphor and the second red phosphor is not limited to this.For example, the KSF phosphor 15 may be used as the first red phosphor,and a SCASN phosphor may be used as the second red phosphor. The SCASNphosphor is represented by the following chemical formula.

Chemical formula of SCASN phosphor . . . (Sr,Ca)AlSiN₃:Eu

Furthermore, the KSF phosphor 15 may be used as the first red phosphor,and an αSiAlON phosphor may be used as the second red phosphor. TheαSiAlON phosphor is represented by the following chemical formula.

Chemical formula of αSiAlON phosphor . . . Ca(Si,Al)₁₂(O,N)₁₆:Eu

FIG. 4 illustrates a light emission state of the red light which isemitted from each of the KSF phosphor 15 and the CASN phosphor 16, in acase where the KSF phosphor 15 is used as the first red phosphor and theCASN phosphor 16 is used as the second red phosphor. However, the secondred phosphor is not limited to the CASN phosphor 16, and a phosphor(second phosphor) which emits red light with an afterglow time that isequal to or shorter than 100 μs may be used instead of the CASN phosphor16.

FIG. 18 is a diagram obtained by simulating light emission states of theblue light and the red light of the LED according to the PWM signal,using the KSF phosphor and a phosphor having an afterglow time which isassumed to be 100 μs.

In FIG. 18, light emission of the LED chip represents a light emissionstate of the blue light which is emitted from the LED chip 13, and lightemission of the red phosphor represents a light emission state of thered light that is emitted from the KSF phosphor 15 in which excitationemission is performed by the blue light emitted from the LED chip 13 anda phosphor which emits the blue light having an afterglow time of 100μs. A frequency and duty of the PWM signal which is supplied from theconstant current circuit 23 to the LED circuit 25 are respectively 120Hz and 25%, and a light intensity ratio between the KSF phosphor 15 andthe phosphor which emits the red light having an afterglow time of 100μs is 50:50.

In the same manner as in FIG. 4, in FIG. 18, a rising edge and a fallingedge of the light emitted from the phosphor containing two types ofphosphors which are the KSF phosphor 15 and the phosphor emitting thered light having an afterglow time of 100 μs are steeper than a risingedge and a falling edge of the light emitted from the red phosphorcomposed of only the KSF phosphor illustrated in FIG. 17.

That is, it can be seen that after the light emission of the LED chip isoff, the afterglow of the red phosphor containing two types of phosphorswhich are the KSF phosphor 15 and the phosphor emitting the red lighthaving an afterglow time of 100 μs that are illustrated in FIG. 18 isreduced more than that of the red phosphor composed of only the KSFphosphor illustrated in FIG. 17.

Since the afterglow time of KSF phosphor (first phosphor) isapproximately 10 ms, the afterglow time of the phosphor (secondphosphor) which emits the red light having an afterglow time of 100 μsis 1/100 of the afterglow time of the KSF phosphor (first phosphor).That is, a response speed of the second phosphor may be equal to orfaster than 100 times the response speed of the first phosphor.

In this way, the second red phosphor (second phosphor) distributed inthe resin 14 may be a phosphor which emits red light having an afterglowtime equal to or less than 100 μs, and a phosphor which emits the redlight using allowed transition satisfies the requirement of the responsetime. It is more preferable to use, as the second red phosphor,particularly a phosphor material in which the afterglow time which isthe time taken for the light intensity to become 1/e is equal to or lessthan 10 μs.

(Main Effects)

As described above, the LED 11 includes the LED chip 13 which emits theblue light as primary light, the resin 14 which seals the LED chip 13,and the KSF phosphor 15 and the CASN phosphor 16 which are distributedin the resin 14, absorb a part of the blue light that is primary light,and emit the red light as secondary light having a wavelength longerthan that of the blue light. In addition, the KSF phosphor 15 absorbsthe blue light which is primary light and emits the red light which issecondary light by the forbidden transition. Meanwhile, the CASNphosphor 16 absorbs the blue light which is primary light and emits thered light which is secondary light by the allowed transition.

For this reason, it is possible to obtain the red light having a narrowwavelength width near a peak wavelength of 630 nm according to the lightemitted from the KSF phosphor 15, as secondary light. For this reason,it is possible to obtain secondary light with high color purity.Meanwhile, it is possible to obtain the fast red light having theafterglow time which is the time t required for the light intensity tobecome 1/e from light intensity at the time of extinguishing primarytime and which is approximately equal to or longer than 1 μs and equalto or shorter than 10 μs, as secondary light by the CASN phosphor 16.For this reason, it is possible to obtain second light having a fastresponse speed. That is, it is possible to obtain the LED 11 having highcolor purity of the red light as secondary light and a fast responsespeed.

In addition, the LED 11 includes the package 12 in which only one cavity12 a that is a concave portion is provided. The LED chip 13 is disposedin the cavity 12 a, and the resin 14 is disposed in the cavity 12 a.

In addition, two types of phosphors which are the KSF phosphor 15 thatemits the red light by the forbidden transition and the CASN phosphor 16that emits the red light by the allowed transition, emit light havingthe same color, and are different from each other, are distributed inthe resin 14.

Accordingly, it is possible to obtain the LED 11 which has one cavity,emits red light having high color purity as secondary light, and has afast response speed.

A wavelength width (wavelength band) of the peak wavelength of the redlight which is secondary light that is emitted from the KSF phosphor 15distributed in the resin 14 is equal to or less than 30 nm. For thisreason, it is possible to obtain red light with high color purity.Furthermore, the afterglow time of the CASN phosphor 16 which is thetime required for the intensity of the secondary light to become 1/ewhen the LED chip 13 extinguishes the primary light which is on, isapproximately equal to or longer than 1 μs and equal to or shorter than10 μs and is equal to or shorter than 100 μs, and a response speed ofthe CASN phosphor 16 is fast. For this reason, it is possible to obtainthe LED 11 which emits red light with high color purity as secondarylight and has a high response speed.

(Additional Matters)

In the first embodiment, it is described that the KSF phosphor 15 andthe CASN phosphor 16 which are red phosphor, and the green phosphor 17are distributed in the resin 14 which seals the LED chip 13.Mn-activated γ-AlON, and β-type SiAlON which is a divalent Eu-activatedoxynitride phosphor or a divalent Eu-activated silicate phosphor may bedistributed as the green phosphor 17.

Accordingly, as described in PTL 3, the Mn-activated γ-AlON of the greenphosphor obtains a narrow spectrum by the phosphor of the forbiddentransition type, but has a delayed response speed, in the same manner asin the KSF phosphor which is a red phosphor. The divalent Eu-activatedoxynitride phosphor or a divalent Eu-activated silicate phosphor of thegreen phosphor has a fast response speed in the same manner as CASNphosphor which is a red phosphor.

Embodiment 2

A second embodiment of the present invention will be described asfollows with reference to FIG. 13 to FIG. 16. In addition, for the sakeof convenience of description, the same symbols will be attached to themembers having the same functions as the members described in theembodiment 1, and description thereof will be omitted.

FIG. 13(a) is an expanded plan view illustrating a part of a lightsource unit 37 in an illumination device 31 according to embodiment 2,and FIG. 13(b) is a sectional view of the illumination device 31.

As illustrated in FIGS. 13(a) and 13(b), the illumination device 31includes the substrate 2, multiple LEDs (light emitting device) 41, andthe light guiding plate 5. In addition, the illumination device 31 alsoincludes an LED drive control unit (refer to FIG. 15), which is notillustrated in FIG. 13, for controlling drive of the multiple LEDs 41.

The multiple LEDs 41 are mounted on the substrate 2 so as be lined up inone line in a longitudinal direction of the substrate 2. In addition,the LED 41 includes two LEDs of an LED chip (first light emittingelement) 43 and an LED chip (second light emitting element) 44 which aredisposed with an interval therebetween.

The LEDs 41 are disposed such that the LED chips 43 on one side of therespective LEDs 41 are lined up in one line in the longitudinaldirection of the substrate 2, and the LED chips 44 on the other side ofthe respective LEDs 41 are lined up in one line in the longitudinaldirection of the substrate 2. In addition, the LEDs 41 are disposed withan interval such that the two LED chips 43 and 44 are lined up in adirection (short-hand direction of the substrate 2) orthogonal to acolumn direction (longitudinal direction of the substrate 2) betweenadjacent columns.

The multiple LED chips 43 which are lined up in the same columndirection (longitudinal direction of the substrate 2) are coupled inseries, and each configures an LED circuit 55 which will be below. Inaddition, the multiple LED chips 44 which are lined up in the samecolumn direction (longitudinal direction of the substrate 2) are coupledin series, and each configures an LED circuit 56 which will be below.

The substrate 2 and the LED 41 configure the light source unit 37. Inthe light source unit 37, a light emitting surface of each of themultiple LEDs 41 faces the light incident portion 5 a and is disposed ata location close to the light guiding plate 5, such that light emittedfrom the LED chips 43 and 44 of each of the multiple LEDs 41 is incidenton the light incident portion 5 a of the light guiding plate 5.

(Configuration of LED 41)

FIG. 14 is a sectional view of the LED 41 in the illumination device 31.The LED 41 includes a package 42, the LED chips 43 and 44, the resin 14,the KSF phosphor 15, the CASN phosphor 16, and the green phosphor 17.

The package 42 includes two concave portions of a first cavity (concaveportion) 42 a and a second cavity (concave portion) 42 b. The firstcavity 42 a is a space which is provided in the package 42, such thatthe LED chip 43 is mounted on a bottom surface in the concave portionand a side surface of the concave portion is used as a reflectingsurface. The second cavity 42 b is a space which is provided in thepackage 42, such that the LED chip 44 is mounted on a bottom surface inthe concave portion and a side surface of the concave portion is used asa reflecting surface.

In the same manner as the package 12 according to the aforementionedEmbodiment 1, the package 42 is formed of a nylon-based material, and isprovided by insert molding such that a lead frame which is notillustrated is exposed on the bottom surface in each of the first cavity42 a and the second cavity 42 b of the package 42. The lead frame isdivided into two parts at an exposed portion in each of the first cavity42 a and the second cavity 42 b.

The package 42 includes a reflecting surface which forms an inner sidesurface of each of the first cavity 42 a and the second cavity 42 b. Itis preferable that the each reflecting surface is formed of a metal filmwith high reflectance including Ag or Al, or white silicone, such thatlight which is emitted from the LED chips 43 and 44 is reflected to theoutside of the LED 41.

Furthermore, the package 42 includes a partition wall 42 c between thefirst cavity 42 a and the second cavity 42 b which are positioned at twoplaces. Light which is emitted from the two LED chips 43 and 44 isblocked by the partition wall 42 c between two LED chips 43 and 44 inthe LED 41. That is, the two LED chips 43 and 44 are chemicallyseparated from each other by the partition wall 42 c.

The LED chip 43 is mounted on a bottom portion of the first cavity 42 awhich is a concave portion on a side of the package 42, the first cavity42 a is filled with the resin 14, and thereby the LED chip 43 is sealed.The KSF phosphor 15 and the green phosphor 17 are distributed in theresin 14 by which the LED chip 43 is sealed.

The LED chip 44 is mounted on a bottom portion of the second cavity 42 bwhich is a concave portion on the other side of the package 42, thesecond cavity 42 b is filled with the resin 14, and thereby the LED chip44 is sealed. The CASN phosphor 16 and the green phosphor 17 aredistributed in the resin 14 by which the LED chip 44 is sealed.

In a case where a light intensity ratio between the KSF phosphor 15 andthe CASN phosphor 16 is 50:50, a mixture ratio (weight %) of the KSFphosphor 15 and the green phosphor 17 is 100:75.7. Meanwhile, a mixtureratio (weight %) of the CASN phosphor 16 and the green phosphor 17 is13.7:75.7. The mixture ratio of the green phosphor 17 is changed bychromaticity of the LED chips 43 and 44.

The LED chip 43 and 44 is, for example, a gallium nitride (GaN) basedsemiconductor light emitting element having a conductive substrate. Abottom electrode is formed on a bottom surface of the conductivesubstrate and an upper electrode is formed on a surface opposite to thebottom surface, which are not illustrated. In the same manner as in theLED chip 13, light (primary light) which is emitted from the LED chips43 and 44 is blue light in a range from 430 nm to 480 nm, and a blue LEDchip having a peak wavelength near 450 nm.

In the LED 41 having the aforementioned configuration, the primary light(blue light) which is emitted from the LED chip 43 on one side passesthrough the resin 14. A part thereof excites the KSF phosphor 15 therebybeing converted into secondary light (red light), and excites the greenphosphor 17 thereby being converted into secondary light (green light).In this way, first white light W1, which is obtained by mixing theprimary blue light and the secondary red and green light from the KSFphosphor 15, is emitted from the first cavity 42 a to the outside of theLED 41.

In the LED 41, the primary light (blue light) which is emitted from thesecond cavity 42 b passes through the resin 14. A part thereof excitesthe CASN phosphor 16 thereby being converted into the secondary light(red light), and excites the green phosphor 17 thereby being convertedinto the secondary light (green light). In this way, second white lightW2, which is obtained by mixing the primary blue light and the secondaryred and green light from the CASN phosphor 16, is emitted from thesecond cavity 42 b of the LED 41 to the outside of the LED 41.

Hence, in the LED 41, white light W4 which is obtained by mixing thefirst white light W1 which is emitted from the first cavity 42 a and thesecond white light W2 which is emitted from the second cavity 42 b isemitted to the outside of the LED 41.

In this way, the LED 41 includes the package 42 in which the firstcavity 42 a and the second cavity 42 b that are multiple concaveportions are provided, the LED chip 43 is disposed on the bottom surfacein the first cavity 42 a, and the LED chip 44 is disposed on the bottomsurface in the second cavity 42 b.

The resin 14 is disposed in each of the first cavity 42 a and the secondcavity 42 b, the KSF phosphor 15 is distributed in the resin 14 which isdisposed in the first cavity 42 a, and the CASN phosphor 16 isdistributed in the resin 14 which is disposed in the second cavity 42 b.Accordingly, it is possible to obtain the LED 41 which includes themultiple cavities of the first cavity 42 a and the second cavity 42 b,and has high color purity of the red light as secondary light and a fastresponse speed.

It is described that the LED 41 has two cavities of the first cavity 42a and the second cavity 42 b which are integrally provided in thepackage 42, but the number of cavities which are provided in the package42 is not limited to two pieces and may be three or more.

In addition, it is described that the LED 41 includes a light emittingunit which emits the first white light W1 and the second white light W2in one package, but a configuration may be provided in which the packageis divided into two packages of one LED that emits the first white lightand the other LED that emits the second white light. That is, the LED 41may have a configuration in which a light intensity ratio between thefirst white light W1 and the second white light W2 can be changed, andmay have a configuration in which the package is configured by two ormore LEDs different from each other.

(Configuration of LED Drive Control Unit 51)

FIG. 15 is a block diagram illustrating a configuration of an LED drivecontrol unit 51 which controls drive of the LED chips 43 and 44.

As illustrated in FIG. 15, the LED drive control unit 51 includes adimming control unit (pulse width modulation signal generation unit) 52,constant current circuits 53 and 54, and LED circuits 55 and 56. The LEDcircuit 55 is a series circuit of the LED chip 43 which is mounted onthe substrate 2. The LED circuit 56 is a series circuit of the LED chip44 which is mounted on the substrate 2.

The dimming control unit 52 independently controls illumination time ofthe LED chips 43 and 44 of the LED circuits 55 and 56 according to PWMcontrol. For this reason, the dimming control unit 52 includes a PWMcircuit (not illustrated) which independently generates a first PWMsignal that is provided to the LED circuit 55 and a second PWM signalthat is provided to the LED circuit 56. The PWM circuit changes a dutyratio of the PWM signals according to instruction from the outside andgenerates the first PWM signal and the second PWM signal.

The constant current circuit 53 generates a constant current which flowsthrough the LED circuit 55, based on the first PWM signal which issupplied from the dimming control unit 52. While the constant currentcircuit 53 is on during a period in which the first PWM signal has an Hlevel thereby supplying a constant current to the LED circuit 55, theconstant current circuit 53 is off during a period in which the firstPWM signal has an L level thereby stopping supply of a constant currentto the LED circuit 55.

The constant current circuit 54 generates a constant current which flowsthrough the LED circuit 56, based on the second PWM signal which issupplied from the dimming control unit 52. While the constant currentcircuit 54 is on during a period in which the second PWM signal has an Hlevel thereby supplying a constant current to the LED circuit 56, theconstant current circuit 54 is off during a period in which the secondPWM signal has an L level thereby stopping supply of a constant currentto the LED circuit 56.

As described above, in the LED drive control unit 51, the dimmingcontrol unit 52 generates the first PWM signal for making the LED chip43 emit light by a pulse width modulation, and the second PWM signal formaking the LED chip 44 emit light by a pulse width modulation. Inaddition, the dimming control unit 52 outputs the generated first PWMsignal to the constant current circuit 53. The constant current circuit53 drives the LED chip 43 by making a current flow through the LEDcircuit 55, based on the first PWM signal which is input from thedimming control unit 52. In addition, the dimming control unit 52outputs the generated second PWM signal to the constant current circuit54. The constant current circuit 54 drives the LED chip 44 by making acurrent flow through the LED circuit 56, based on the second PWM signalwhich is input from the dimming control unit 52.

In this way, the constant current circuit 53 controls the current whichflows through the LED circuit 55 according to the first PWM signal whichis independently controlled by the dimming control unit 52. In addition,the constant current circuit 54 controls the current which flows throughthe LED circuit 56 according to the second PWM signal. Accordingly,light intensity of the LED chips 43 and 44 are independently controlled.

For this reason, it is possible to independently adjust intensity of thefirst white light W1 which is obtained by mixing the primary light fromthe LED chip 43 and the secondary light which is emitted from the KSFphosphor 15 that absorbs the primary light, and intensity of the secondwhite light W2 which is obtained by mixing the primary light from theLED chip 44 and the secondary light which is emitted from the CASNphosphor 16 that absorbs the primary light. Accordingly, it is possibleto obtain the light source unit 37 with wide color reproducibility and ahigh response speed.

(Illumination Control of LED Chips 43 and 44)

FIG. 16 is a diagram illustrating a relationship between the PWM signaland drive states of the LED chips 43 and 44. In FIG. 16, states (1) to(4) represent the following states.

State (1): a case where it is required that the LED chip 43 isilluminated and the LED chip 44 is not illuminated.

State (2): a case where it is required that the LED chip 43 is notilluminated and the LED chip 44 is illuminated.

State (3): a case where it is required that both the LED chips 43 and 44are illuminated together.

State (4): a case where it is required that both the LED chips 43 and 44are not illuminated together.

As described in FIG. 16, when state (1) is required, the PWM circuitincluded in the dimming control unit 52 generates the PWM signal whichmakes the LED chip 43 go into an H level, and the PWM signal which makesthe LED chip 44 go into an L level. The PWM circuit respectively outputsthe respectively generated PWM signals to the constant current circuits53 and 54. The constant current circuit 53 makes a constant current flowthrough the LED circuit 55, based on the PWM signal having an H levelwhich is output from the PWM circuit, and lights the LED chip 43.Meanwhile, the constant current circuit 54 does not make a constantcurrent flow through the LED circuit 55, based on the PWM signal havingan L level which is output from the PWM circuit, and does not light theLED chip 44. Accordingly, the white light W4 which is configured by onlythe first white W1 including the red light that is emitted from the KSFphosphor 15 is emitted from the first cavity 42 a to the outside of theLED 41.

At the time of state (2), the PWM circuit generates the PWM signal whichmakes the LED chip 43 go into an L level, and the PWM signal which makesthe LED chip 44 go into an H level. The PWM circuit respectively outputsthe respectively generated PWM signals to the constant current circuits53 and 54. The constant current circuit 53 does not make a constantcurrent flow through the LED circuit 55, based on the PWM signal havingan H level which is output from the PWM circuit, and does not light theLED chip 43. Meanwhile, the constant current circuit 54 makes a constantcurrent flow through the LED circuit 55, based on the PWM signal havingan H level which is output from the PWM circuit, and lights the LED chip44. Accordingly, the white light W4 which is configured by only thesecond white W2 including the red light that is emitted from the CASNphosphor 16 is emitted from the second cavity 42 b to the outside of theLED 41.

At the time of state (3), the PWM circuit generates the PWM signal whichmakes the LED chip 43 go into an H level, and the PWM signal which makesthe LED chip 44 go into an H level. The PWM circuit respectively outputsthe respectively generated PWM signals to the constant current circuits53 and 54. The constant current circuit 53 makes a constant current flowthrough the LED circuit 55, based on the PWM signal having an H levelwhich is output from the PWM circuit, and lights the LED chip 43.Meanwhile, the constant current circuit 54 makes a constant current flowthrough the LED circuit 56, based on the PWM signal having an H levelwhich is output from the PWM circuit, and lights the LED chip 44.Accordingly, the white light W4 which is configured by the first whiteW1 including the red light that is emitted from the KSF phosphor 15 andthe second white W2 including the red light that is emitted from theCASN phosphor 16 is emitted from the first cavity 42 a and the secondcavity 42 b to the outside of the LED 41.

At the time of state (4), the PWM circuit generates the PWM signal whichmakes the LED chip 43 go into an L level, and the PWM signal which makesthe LED chip 44 go into an L level. The PWM circuit respectively outputsthe respectively generated PWM signals to the constant current circuits53 and 54. The constant current circuit 53 does not make a constantcurrent flow through the LED circuit 55, based on the PWM signal havingan L level which is output from the PWM circuit, and does not light theLED chip 43. Meanwhile, the constant current circuit 54 does not make aconstant current flow through the LED circuit 56, based on the PWMsignal having an L level which is output from the PWM circuit, and doesnot light the LED chip 44. Accordingly, the LED 41 is not illuminated.

The dimming control unit 52 changes current setting values of theconstant current circuit 53 and the constant current circuit 54 therebybeing able to control intensity of light which is emitted from the LEDcircuit 55 and the LED circuit 56, and a ratio of light quantity betweenthe first white W1 and the second white W2 can also be arbitrarilycontrolled.

As the dimming control unit 52 controls drive current values of the LEDcircuits 55 and 56 and a duty ratio of the PWM signal, it is possible toeasily change a ratio of amount of light between the first white W1 andthe second white W2.

Here, in the present embodiment, the illumination device 31 (refer toFIG. 13) and a display panel which is illuminated by the illuminationdevice 31 are provided, and thus, for example, the following mode (firstmode) A and mode (second mode) B are used as a display mode which isrequired for a display device such as a liquid crystal television thatis used for the illumination device 31.

Mode A: a case where clear image quality is required rather than aresponse speed.

Mode B: a case where a response speed is required rather than clearimage quality.

In mode A, the dimming control unit 52 in the illumination device 31increases the amount of the first white W1 and decreases the amount ofthe second white W2. Alternatively, the illumination device 31 decreasesthe amount of the second white W2 to zero. That is, the dimming controlunit 52 does not light the LED chip 44, but decreases the amount oflight of the LED chip 44 more than that of the LED chip 43, andincreases the amount of light of the LED chip 43 more than that of theLED chip 44. Accordingly, the LED chip 43 emits the amount of light morethan that of the LED chip 44. As a result, the display device candisplay clearer images.

In mode B, the dimming control unit 52 in the illumination device 31decreases the amount of the first white W1 and increases the amount ofthe second white W2 more than that of the first white W1. Alternatively,the illumination device 31 decreases the amount of the first white W1 tozero. That is, the dimming control unit 52 does not light the LED chip43, but decreases the amount of light of the LED chip 43 more than thatof the LED chip 44, and increases the amount of light of the LED chip 44more than that of the LED chip 43. By doing so, the LED chip 44 emitsthe amount of light more than that of LED chip 43. As a result, thedisplay device can display images at a faster response speed.

As described above, the mode A and the mode B which are required for adisplay device of a liquid crystal television or the like for which theillumination device 31 is used can also be realized by the illuminationdevice 31.

In the second embodiment, it is described that the KSF phosphor 15 usedas a red phosphor and the green phosphor 17 are distributed in the resin14 which seals the LED chip 43, and the CASN phosphor 16 used as a redphosphor and the green phosphor 17 are distributed in the resin 14 whichseals the LED chip 44. However, the KSF phosphor 15 used as a redphosphor and Mn-activated γ-AlON used as a green phosphor may bedistributed in the resin 14 which seals the LED chip 43, and the CASNphosphor 16 used as a red phosphor and β-type SiAlON which is a divalentEu-activated oxynitride phosphor used as a green phosphor or a divalentEu-activated silicate phosphor may be distributed in the resin 14 whichseals the LED chip 44.

Embodiment 3

A third embodiment of the present invention will be described asfollows. In addition, for the sake of convenience of description, thesame symbols will be attached to the members having the same functionsas the members described in the embodiments 1 and 2, and descriptionthereof will be omitted.

In a case of a drive state in which duty of the signal which is used inthe LED 11 (refer to FIG. 1) described in embodiment 1 or the LED 41(refer to FIG. 14) described in embodiment 2 is equal to or less than50%, the mixture ratio of the KSF phosphor 15 and the CASN phosphor 16is adjusted according to the frequency of the PWM signal. Accordingly,it is possible to improve video quality of a display device such as aliquid crystal television which uses the LED 11 or the LED 41.

(a) When the Frequency (Frame Frequency) of the PWM Signal is Equal toor Higher than 60 Hz and Lower than 120 Hz

In the display device, the frequencies (frame frequencies) of the PWMsignals of the illumination devices 1 and 31 are set to be equal to orhigher than 60 Hz and lower than 120 Hz. In this case, a light intensityratio (peak ratio of light spectrum) between the KSF phosphor 15 and theCASN phosphor 16 in the LED 11 or the LED 41 needs to be KSF:CASN=20:80.

In a case where the illumination device 1 in which the LED 11 having onecavity per package that is described in embodiment 1 is manufactured,the KSF phosphor 15 and the CASN phosphor 16 are distributed in theresin 14 in a manufacturing process of the LED 11 such that a mixtureratio (weight %) of the KSF phosphor 15 and the CASN phosphor 16 isKSF:CASN=40:21.9. By doing so, the light intensity ratio (peak ratio oflight spectrum) between the KSF phosphor 15 and the CASN phosphor 16 inthe LED 11 can be KSF:CASN=20:80.

Meanwhile, in embodiment 2, a light intensity ratio between white lights(first white W and second white W) from two light sources is changed bychanging a duty ratio of PWM or an LED drive current value. Accordingly,in embodiment 2, it is possible to appropriately switch the lightintensity ratio according to an operation mode of a television, andfurthermore, to obtain merit such as finely setting a light amountratio.

In embodiment 2, it is described that, in manufacturing conditions ofthe LED 41, the mixture ratio of the phosphors respectively distributedin the first cavity 42 a and the second cavity 42 b is set to a ratio inwhich a light intensity ratio at the time of driving the two lightsources (LED chips 43 and 44) in the same conditions is 50:50. Inaddition, by changing a duty ratio or a drive current, the lightintensity ratio between the first cavity 42 a and the second cavity 42 bcan be changed.

In a case where the illumination device 1 in which the LED 41 having twocavities per package that is described in embodiment 2 is manufactured,the illumination device 1 is realized by controlling the PWM signal inwhich an intensity ratio of peak wavelength between the first whitelight W1 and the second white light W2 is 20:80, or the LED drivecurrent.

In a manufacturing process of the LED 41, the KSF phosphor 15 and thegreen phosphor 17 are distributed in the resin 14 such that a mixtureratio (weight %) of the KSF phosphor 15 and the green phosphor 17 isKSF:green phosphor=100:75.7. By doing so, the KSF phosphor 15 and thegreen phosphor 17 are distributed in the resin 14 which seals the firstcavity 42 a such that KSF:green phosphor=100:75.7.

Furthermore, in a manufacturing process of the LED 41, the CASN phosphor16 and the green phosphor 17 are distributed in the resin 14 such that amixture ratio (weight %) of the CASN phosphor 16 and the green phosphor17 is CASN:green phosphor=13.7:75.7. By doing so, the CASN phosphor 16and the green phosphor 17 are distributed in the resin 14 which sealsthe second cavity 42 b such that CASN:green phosphor=13.7:75.7.

The other manufacturing processes of the LED 41 are the same as themanufacturing processes of the LED having two cavities per normalpackage. The LED 41 which is obtained by doing so is mounted in theillumination device 31.

Furthermore, the dimming control unit 52 (refer to FIG. 15) generatesthe first PWM signal and the second PWM signal such that an intensityratio between a peak wavelength of the red wavelength components of thefirst white light W1 and a peak wavelength of the red wavelengthcomponents of the second white light W2 is 20:80, outputs the first PWMsignal to the constant current circuit 53, and outputs the second PWMsignal to the constant current circuit 54. The constant current circuit53 outputs a constant current based on the first PWM signal which isinput from the dimming control unit 52 to the LED circuit 55, and theconstant current circuit 54 outputs a constant current based on thesecond PWM signal which is input from the dimming control unit 52 to theLED circuit 56.

In a case where the illumination device 1 is manufactured at the mixtureratio (weight %) of the phosphor described above, if the LED chip 43 andthe LED chip 44 are illuminated in the same drive conditions as eachother, the first white light W1 and the second white light W2 areemitted at a light intensity ratio of peak wavelength of 50:50. Here, inthe dimming control unit 52, if a ratio between the duty ratios of thefirst PWM signal and the second PWM signal is 20:80, the intensity ratioof peak wavelength between the first white light W1 and the second whitelight W2 is 20:80. An LED drive current value may be set, such that acurrent having a current value in which light brightness of the LED chip43 and the LED chip 44 is 20:80 is output from the constant currentcircuit 53 and the constant current circuit 54, in accordance with aforward current of the LED chip vs characteristics of light brightness.

It is needless to say that, even in a case where the mixture ratios ofthe phosphors are different from each other, if the duty ratio of thePWM signal or an LED drive current value is appropriately set, lightintensity in which the intensity ratio of peak waveform between thefirst white light W1 and the second white light W2 is 20:80 can berealized in the same manner.

As described above, the light intensity ratio (peak ratio of lightspectrum) between the KSF phosphor 15 and the CASN phosphor 16 in theLED 41 can be KSF:CASN=20:80.

(b) When the Frequency (Frame Frequency) of the PWM Signal is Equal toor Higher than 120 Hz and Equal to or Lower than 240 Hz

In the display device, the frequencies (frame frequencies) of the PWMsignals of the illumination devices 1 and 31 are set to be equal to orhigher than 120 Hz and equal to or lower than 240 Hz. In this case, alight intensity ratio (peak ratio of light spectrum) between the KSFphosphor 15 and the CASN phosphor 16 in the LED 11 or the LED 41 needsto be KSF:CASN=50:50.

In a case where the illumination device 1 in which the LED 11 having onecavity per package that is described in embodiment 1 is manufactured,the KSF phosphor 15 and the CASN phosphor 16 are distributed in theresin 14 in a manufacturing process of the LED 11 such that a mixtureratio (weight %) of the KSF phosphor 15 and the CASN phosphor 16 isKSF:CASN=100:13.7. By doing so, the light intensity ratio (peak ratio oflight spectrum) between the KSF phosphor 15 and the CASN phosphor 16 inthe LED 11 can be KSF:CASN=50:50.

In a case where the illumination device 1 in which the LED 41 having twocavities per package that is described in embodiment 2 is manufactured,the illumination device 1 is realized by controlling the PWM signal inwhich an intensity ratio of peak wavelength between the first whitelight W1 and the second white light W2 is 50:50, or the LED drivecurrent.

In a manufacturing process of the LED 41, the KSF phosphor 15 and thegreen phosphor 17 are distributed in the resin 14 such that a mixtureratio (weight %) of the KSF phosphor 15 and the green phosphor 17 isKSF:green phosphor=100:75.7. By doing so, the KSF phosphor 15 and thegreen phosphor 17 are distributed in the resin 14 which seals the firstcavity 42 a such that KSF:green phosphor=100:75.7.

Furthermore, in a manufacturing process of the LED 41, the CASN phosphor16 and the green phosphor 17 are distributed in the resin 14 such that amixture ratio (weight %) of the CASN phosphor 16 and the green phosphor17 is CASN:green phosphor=13.7:75.7. By doing so, the CASN phosphor 16and the green phosphor 17 are distributed in the resin 14 which sealsthe second cavity 42 b such that CASN:green phosphor=13.7:75.7.

The other manufacturing processes of the LED 41 are the same as themanufacturing processes of the LED having two cavities per normalpackage. The LED 41 which is obtained by doing so is mounted in theillumination device 31.

Furthermore, the dimming control unit 52 (refer to FIG. 15) generatesthe first PWM signal and the second PWM signal such that an intensityratio between a peak wavelength of the red wavelength components of thefirst white light W1 and a peak wavelength of the red wavelengthcomponents of the second white light W2 is 50:50, outputs the first PWMsignal to the constant current circuit 53, and outputs the second PWMsignal to the constant current circuit 54. The constant current circuit53 outputs a constant current based on the first PWM signal which isinput from the dimming control unit 52 to the LED circuit 55. Theconstant current circuit 54 outputs a constant current based on thesecond PWM signal which is input from the dimming control unit 52 to theLED circuit 56.

In a case where the illumination device 1 is manufactured at the mixtureratio (weight %) of the phosphor described above, if the LED chip 43 andthe LED chip 44 are illuminated in the same drive conditions as eachother, the first white light W1 and the second white light W2 areemitted at a light intensity ratio of peak wavelength of 50:50. In thiscase, in the dimming control unit 52, if the first PWM signal and thesecond PWM signal have the same duty ratio and the LED drive signalswhich are output from the constant current circuits 53 and 54 are set tothe same value, the intensity ratio of peak wavelength between the firstwhite light W1 and the second white light W2 is 50:50.

In addition, it is needless to say that, even in a case where themixture ratios of the phosphors are different from each other, if theduty ratio of the PWM signal or an LED drive current value isappropriately set, light intensity in which the intensity ratio of peakwaveform between the first white light W1 and the second white light W2is 50:50 can be realized in the same manner.

As described above, the light intensity ratio (peak ratio of lightspectrum) between the KSF phosphor 15 and the CASN phosphor 16 in theLED 41 can be KSF:CASN=50:50.

(c) When the Frequency (Frame Frequency) of the PWM Signal is Equal toor Higher than 240 Hz

If the frequency of the PWM signal is equal to or higher than 240 Hz,coloring phenomenon due to afterglow is hardly noticeable, and thus,only the KSF phosphor 15 can be used as a red phosphor, but it is morepreferable that the KSF phosphor 15 and the CASN phosphor 16 which arecombined together are used.

Reduction of coloring phenomenon such as a telop being displayed on ascreen of a television which is caused by increasing the frequency ofthe PWM signal is due to the fact that an ON period in which threecolors of blue, green, and red are output and an OFF period in whichonly the afterglow of red remains are shortened and an interval is alsoreduced. Accordingly, the following two reasons (1) and (2) areconsidered.

(1) Even though telops are displayed on a screen, if time in which onlyred afterglow is emitted is reduced, a width of an area in whichafterglow color is shown in telop characters is reduced and it isdifficult to view the telops.

(2) An interval in which an ON period during which three colors of blue,green, and red are output and an OFF period during which only afterglowof red remains are repeated is reduced, and thus, human eyes hardly seethe color in a separated manner due to afterimage.

Generally, a display device which displays the television broadcast doesnot drive the frequency of the PWM signal at a frequency not more than60 Hz.

CONCLUSION

The light emitting device according to aspect 1 of the present inventionincludes a light emitting element which emits primary light; a resinwhich seals the light emitting element; and first and second phosphorswhich are distributed in the resin, absorb part of the primary light,and emit secondary light having a wavelength longer than that of theprimary light. The first phosphor absorbs the primary light and emitsthe secondary light by forbidden transition. The second phosphor absorbsthe primary light and emits the secondary light by allowed transition.

According to the aforementioned configuration, the secondary lighthaving a narrow width of peak wavelength of a light wavelength isobtained by the first phosphor. In addition, the secondary light havinga fast response speed is obtained by the second phosphor. Accordingly,it is possible to obtain a light emitting device which emits thesecondary light with high color purity and has a fast response speed.

The light emitting device according to aspect 2 of the presentinvention, in the aspect 1, may include a package in which only onecavity that is a concave portion is provided. The light emitting elementmay be disposed on a bottom surface in the cavity. The resin may bedisposed in the cavity, and the first and second phosphors may bedistributed in the resin. By using the configuration, it is possible toobtain a light emitting device which includes one cavity, emits thesecondary light with high color purity, and has a fast response speed.

The light emitting device according to aspect 3 of the presentinvention, in the aspect 1, may include a package in which first andsecond cavities that are multiple concave portions are provided. Thelight emitting element may include a first light emitting element whichis disposed on a bottom surface in the first cavity, and a second lightemitting element which is disposed on a bottom surface in the secondcavity. The resin may be disposed in the first and second cavities. Thefirst phosphor may be distributed in the resin which is disposed in thefirst cavity. The second phosphor may be distributed in the resin whichis disposed in the second cavity. By using the aforementionedconfiguration, it is possible to obtain a light emitting device whichincludes the first and second cavities that are multiple cavities, emitsthe secondary light with high color purity, and has a fast responsespeed.

According to the light emitting device of aspect 4 of the presentinvention, in the aspect 3, when a display panel which is illuminated bythe light emitting device displays an image in a first mode, as adisplay mode of the display panel, of two of the first mode in which aclear image quality is required over a response speed and a second modein which the response speed is required over the clear image quality,the first light emitting element may emit light having amount more thanthat of the second light emitting element. By using the aforementionedconfiguration, it is possible to display a clearer image.

According to the light emitting device of aspect 5 of the presentinvention, in the aspect 3, when a display panel which is illuminated bythe light emitting device displays an image in a second mode, as adisplay mode of the display panel, of two of a first mode in which aclear image quality is required over a response speed and the secondmode in which the response speed is required over the clear imagequality, the second light emitting element may emit light having amountmore than that of the first light emitting element. By using theaforementioned configuration, it is possible to display an image withfaster response speed.

An illumination device according to aspect 6 of the present inventionmay include the light emitting device in the aspects 1 to 5. By usingthe aforementioned configuration, it is possible to obtain anillumination device which emits the secondary light with high colorpurity and has a fast response speed.

According to a light emitting device of another aspect of the presentinvention, in the aforementioned aspects, if a wavelength band of peakwavelength of the secondary light which is emitted from the firstphosphor is equal to or less than 30 nm, and the time required for theintensity of the secondary light to become 1/e (e is a natural logarithmbase) when the light emitting element extinguishes the primary lightwhich is on is referred to as afterglow time, an afterglow time of thesecond phosphor may be equal to or less than 1/100 of an afterglow timeof the first phosphor. By the aforementioned configuration, a lightemitting device which emits the secondary light with high color purityand has a fast response speed can be obtained.

According to a light emitting device of still another aspect of thepresent invention, in the aforementioned aspects, the first phosphor maycontain tetravalent manganese-activated fluoride tetravalent metal saltphosphor. By the aforementioned configuration, the first phosphor as anaspect can be obtained.

According to a light emitting device of still another aspect of thepresent invention, in the aforementioned aspects, the light emittingelement may be a gallium nitride-based semiconductor which emits theprimary light having a peak wavelength equal to or higher than 430 nmand equal to or shorter than 480 nm. By the aforementionedconfiguration, the light emitting element as an aspect can be obtained.

According to a light emitting device of still another aspect of thepresent invention, in the aforementioned aspects, the second phosphormay contain a divalent Eu-activated CaAlSiN₃ structure. By theaforementioned configuration, the second phosphor as an aspect can beobtained.

According to a light emitting module of still another aspect of thepresent invention, in the aforementioned aspects, may include the lightemitting device and pulse width modulation signal generation means whichgenerates a first pulse width modulation signal for making the firstlight emitting element emit light by pulse width modulation, and asecond pulse width modulation signal for making the second lightemitting element emit light by pulse width modulation.

By the aforementioned configuration, drive control of the first lightemitting element and the second light emitting element can beindependently made. Accordingly, it is possible to independently adjustintensity of mixture light of primary light from the first lightemitting element and secondary light which is emitted from the firstphosphor that absorbs the primary light, and intensity of mixture lightof primary light from the second light emitting element and secondarylight which is emitted from the second phosphor that absorbs the primarylight. Accordingly, it is possible to obtain a light emitting modulewith wide color reproducibility and a fast response speed.

The present invention is not limited to the aforementioned eachembodiment, various modifications can be made in a range described inthe claims, and an embodiment which is obtained by appropriatelycombining technical means that are respectively disclosed in otherembodiments is also included in a technical range of the presentinvention. Furthermore, it is possible to configure novel technicalcharacteristics by combining the technical means which are respectivelydisclosed in each embodiment.

INDUSTRIAL APPLICABILITY

The present invention can be used for a light emitting device and anillumination device.

REFERENCE SIGNS LIST

1⋅31 ILLUMINATION DEVICE

5 LIGHT GUIDING PLATE

7⋅37 LIGHT SOURCE UNIT

11⋅41 LED (LIGHT EMITTING DEVICE)

12⋅42 PACKAGE

12 a CAVITY

13 LED CHIP (LIGHT EMITTING ELEMENT)

14 RESIN

15 KSF PHOSPHOR (FIRST PHOSPHOR)

16 CASN PHOSPHOR (SECOND PHOSPHOR)

17 GREEN PHOSPHOR

21⋅51 LED DRIVE CONTROL UNIT

22⋅52 DIMMING CONTROL UNIT (PULSE WIDTH MODULATION SIGNAL GENERATIONMEANS)

23 CONSTANT CURRENT CIRCUIT

25 LED CIRCUIT

42 a FIRST CAVITY

42 b SECOND CAVITY

42 c PARTITION WALL

43 LED CHIP (FIRST LIGHT EMITTING ELEMENT)

44 LED CHIP (SECOND LIGHT EMITTING ELEMENT)

53⋅54 CONSTANT CURRENT CIRCUIT

55⋅56 LED CIRCUIT

W0 WHITE LIGHT

W1 FIRST WHITE LIGHT

W2 SECOND WHITE LIGHT

W4 WHITE LIGHT

1. A light emitting device comprising: a light emitting element whichemits primary light; a resin which seals the light emitting element; anda first phosphor and a second phosphor that absorb a portion of theprimary light, and emit secondary light having a wavelength longer thanthat of the primary light, wherein the first phosphor absorbs theprimary light and emits the secondary light by forbidden transition, thesecond phosphor absorbs the primary light and emits the secondary lightby allowed transition, a wavelength width of a peak wavelength of alight spectrum of the secondary light emitted by the first phosphor isnarrower than that of a peak wavelength of a light spectrum of thesecondary light emitted by the second phosphor, and a response speed ofthe second phosphor is faster than that of the first phosphor.
 2. Thelight emitting device according to claim 1, wherein the first phosphoris a phosphor having an Mn-activated γ-AlON structure, and the secondphosphor is a divalent Eu-activated oxynitride phosphor or a divalentEu-activated silicate phosphor.
 3. The light emitting device accordingto claim 2, wherein the first phosphor further includes a phosphorhaving an Mn⁴⁺-activated K₂SiF₆ structure.
 4. The light emitting deviceaccording to claim 2, wherein the second phosphor further includes aphosphor having a divalent Eu-activated CaAlSiN₃ structure.
 5. The lightemitting device according to claim 1, wherein the first phosphor is aphosphor having an Mn⁴⁺-activated K₂SiF₆ structure, and the secondphosphor is a phosphor having a divalent Eu-activated CaAlSiN₃structure.
 6. The light emitting device according to claim 5, whereinthe first phosphor further includes a phosphor having an Mn-activatedγ-AlON structure.
 7. The light emitting device according to claim 5,wherein the second phosphor further includes a divalent Eu-activatedoxynitride phosphor or a divalent Eu-activated silicate phosphor.
 8. Thelight emitting device according to claim 6, wherein the second phosphorfurther includes a divalent Eu-activated oxynitride phosphor or adivalent Eu-activated silicate phosphor.
 9. An illumination devicecomprising: the light emitting device according to claim
 1. 10. A liquidcrystal television comprising: the illumination device according toclaim
 9. 11. The light emitting device according to claim 1, whereinintensity of the peak wavelength of the light spectrum of the secondarylight emitted by the second phosphor accounts for not less than 25% andnot more than 50% of a total of (i) an intensity of the peak wavelengthof the light spectrum of the secondary light emitted by the firstphosphor and (ii) an intensity of the peak wavelength of the lightspectrum of the secondary light emitted by the second phosphor.
 12. Thelight emitting device according to claim 1, wherein the first phosphorand the second phosphor are each made of a red phosphor.
 13. The lightemitting device according to claim 1, further comprising: a packageincluding a concave cavity, wherein the light emitting element is on abottom surface in the cavity, and the resin is in the cavity.